In recent years, in a solid-state imaging device, the dynamic range of pixels is narrowed due to increase of the number of the pixels and miniaturization of a pixel. The output of the solid-state imaging device is easily saturated in charges depending on an amount of light incident on a portion having a high brightness of an object. Examples of a countermeasure against the output saturation in charges may include reduction of the output gain, shortening of a charge accumulation time, and the like. In this case, the output saturation in charges can be reduced in the portion having a high brightness; on the other hand, it is difficult to obtain an optimal output in a portion having a low brightness.
High dynamic range (HDR) synthesis is known as an image capturing technique for representing a wider dynamic range than that of a general image capturing method. As an HDR synthesis method, for example, the charge accumulation time and the output gain are differently set in each of horizontal lines in which pixels are arranged in parallel in a horizontal direction. According to this method, a resolution in a vertical direction is substantially decreased by half as compared with a general image capturing method so that the resolution is lowered.
Further, as another HDR synthesis method, for example, two or more images which are obtained by differently setting the charge accumulation time and the output gain are synthesized. According to this method, delay occurs in a frame rate of a synthetic image with respect to an output cycle by an image sensor. Therefore, specifically, when a moving image is captured, object image shake (motion blurring) easily occurs. Further, a frame memory which synchronizes a frame timing for a plurality of images is required so that the size of a circuit is increased, which causes the increase of costs and the increase of power consumption.
As for such a problem, for example, the solid-state imaging device may be taken measures such that a general one pixel is configured as a small pixel group formed of a plurality of small pixels. A small pixel suitable for an optimal output is selected in a signal processing from the small pixel group including a plurality of small pixels having different optical sensitivities and the selected pixel is used for the output. In this method, as compared with a general case where signal charges for every pixel are read, the amount of signals read out from a pixel array is increased so that it is difficult to readout the signal charges at a high speed. In the solid-state imaging device, it is difficult to read out the signal charges from the pixel array at a high speed so that the frame rate is lowered.